Cartonboard properties

Opacity

Opacity is a measurement of the capacity of cartonboard to obscure what lies behind it, and is expressed as a percentage. A high percentage corresponds to a cartonboard sheet with low transparency (high opacity). A cartonboard sheet with 100% opacity is completely opaque. The degree of opacity depends on how well the light is scattered and absorbed by the cartonboard. High opacity is important when printing is done on both sides of the cartonboard sheet.

Gloss

The more light which is reflected by the cartonboard surface, the higher the gloss. Gloss can be achieved with various varnishing methods.

Whiteness

The cartonboard's visual impression of whiteness. Whiteness is expressed by means of a single value.

Brightness

Brightness is a concept used in two different contexts:

# When referring to image reproduction, brightness describes the intensity of the colours. This is also called luminance, i.e. how light or dark an image is.# When referring to cartonboard, brightness is expressed as the percentage of light which is reflected from a cartonboard surface at a wavelength of 457 nm (nm = nanometre).

Flatness

The cartonboard's ability to remain flat (retain its shape) during printing and converting.

Dimensional Stability

Resistance to dimensional changes in a cartonboard sheet due to changes in such properties as moisture content. Dimensional stability is important during printing and conversion to avoid such errors as misregister (see also "REGISTER").

Surface Smoothness

A measurement of how smooth the cartonboard surface is. A smooth cartonboard surface is important for achieving satisfactory printing and varnishing results.

Surface Strength

The cartonboard's ability to tolerate forces on its surface, for instance from the tackiness of the ink during printing. This is important so that the cartonboard surface is not torn away by the printing ink during the printing process.

Tear Strength

The force required to tear a cartonboard sheet along an existing incision. This is important, for example so that a tear strip will work when packaging is being opened.

Compression Strength

When cartons are stacked on top of each other the bottom layer naturally bears the greatest load. To avoid the cartons collapsing, the most important property of cartonboard as a material is good compression strength.

Stiffness

Stiffness is one of the most important properties of cartonboard. The demand for stiffness recurs throughout the entire chain from shipping via the store shelf to the consumer. Cartonboard is the only material which has this ability to offer high stiffness per unit of weight. Without stiffness cartonboard could not fulfil its primary function, which is to protect the contents of the packaging.

Machine Direction

When cartonboard is manufactured the pulp fibres are aligned parallel to the direction in which the cartonboard web is moving. This means that cartonboard is always stiffer and stronger in that direction. The machine direction is therefore at right angles to the width of the web. In terms of creasability, a crease across the machine direction is better than a crease parallel to the machine direction (See "Creasing").

Bulk

Cartonboard which is bulky (voluminous) in relation to its weight is said to have high bulk. Compact cartonboard has low bulk. Cartonboard with high bulk generally feels stiffer and thicker than cartonboard with the same grammage but with low bulk.

Density

Describes how compact the cartonboard is, measured in kilograms per cubic metre (kg/m^3^).

Thickness

The distance between the two surfaces of the cartonboard sheet measured in thousandths of a millimetre (µm). The material used in most cartonboard packaging has a thickness of 350 to 800 µm.

Grammage

The weight of the cartonboard in grams per square metre (g/m²). Paper with a grammage of more than 160 g/m² is normally called cartonboard, since it is first at that level that a fibre-based material can be sufficiently stiff and sturdy to function as packaging. Most cartonboard packaging has a grammage in the range of 200 to 500 g/m².

Printing methods

Offset

Offset is the most common printing method for cartonboard. The most frequently used method is sheet-fed offset, in which the printing press is fed with cartonboard sheets. This contrasts to web offset, which is reel fed. Offset is an indirect printing method, that is, the ink is not transferred to the cartonboard sheet directly from the printing plate. The printing cylinder sets off (hence "offset") the printing ink onto a rubber-covered blanket cylinder, which transfers the ink/printing image to the cartonboard sheet. "Offset" usually refers to offset lithography, a printing method in which the image areas to be printed are distinguished from the nonimage areas by the use of chemical properties rather than differences in level.

Digital Printing

A printing press which prints information directly from a computer in a similar way to a computer printer. There is therefore no need to produce film or a printing plate. The advantages are speed and low costs for small four-colour print runs.

Flexography

In this direct printing method the image areas to be printed are raised above the non-image ones. The printing plate is made of rubber or plastic. The advantage of flexography is that it can be used to print on most materials. Water-based printing inks can be used. The disadvantage is that flexography often has difficulty reproducing all colour hues.

Gravure

Gravure is a direct printing method in which the image areas to be printed are made up of many small recesses which are engraved on a copper printing cylinder and are filled with ink. Gravure printing presses are reel-fed presses which print at very high speeds. Gravure is best suited to long print runs due to the high initial cost and low unit cost. The method gives good image reproduction.

Letterpress

In this printing method the ink is applied onto the raised types of the printing cylinder and then transferred to the cartonboard surface. The letters on the "unprinted" cartonboard samples have been printed using the letterpress method.

Finishing

Folding/Erecting

A die-cut and creased cartonboard blank is made into a carton (see DIE CUTTING and CREASING).

Folding without prior creasing

When a cartonboard sheet is folded without a preexisting crease or scoring (see CREASING and SCORING). This is usually done in a folding machine.

Hot foil stamping

A text or pattern in metallic foil is applied to the cartonboard with the aid of heat, often in combination with embossing.

Embossing

A text or pattern in metallic foil is applied to the cartonboard with the aid of heat, often in combination with embossing.

Creasing

To facilitate folding a well-defined folding line or crease is made. A perfect crease can be compared to a hinge and its aim is to produce the desired shape and function in a carton or in printed material. This binder has two well-defined creases along its spine.

Perforation

A row of punched holes which make it easier to tear off e.g. a coupon or reply card

Nicks

Nicks are non-die-cut sections which hold the blanks together to facilitate handling during the subsequent conversion process.

Die cutting

Die cutting occurs when the cartonboard sheet is cut into a shape, e.g. to create a blank which can be folded and erected to form a carton. After printing, die cutting, and creasing are done simultaneously in a diecutting machine. Die cutting and creasing can be combined with embossing (see EMBOSSING).

Scoring

A fine line is scored in the cartonboard to create a flexible hinge. A scored line is less durable than a crease line (see CREASING).

Pasting

To join two or more cartonboard sheets with adhesive or wax to create a single unit. This binder is constructed in this way.

Lamination

The printed sheet is coated with a protective layer of plastic or metal foil - the laminate. There are gloss and matt laminates. They are applied by a special lamination machine. The laminate provides excellent protection against dirt, moisture and wear. Lamination can also be done for aesthetic reasons. The binder you are holding is laminated on the outside.

Printing terms

Screen Ruling

Screen ruling (also called screen frequency or half-tone resolution) is the number of screen lines per unit of length. It is measured in lines per inch (lpi). The higher the lpi, the greater the amount of detail in an image. The kind of cartonboard and the choice of printing method govern the screen ruling that can be used during printing.

Half-Tone Printing

Printing in which the colour images are in the form of small dots (known as half-tone dots and forming a half-tone screen). The size of the dots determines the colour intensity. The combination of different colours creates a multitude of hues.

Register

When all printing inks are in exact alignment relative to each other, e.g. the separate colour images in fourcolour printing, or during subsequent die-cutting, cutting, embossing etc. Misregister occurs when the separate colour images are not printed exactly on top of each other. Misregister creates unclear images, discoloured edges, etc. To avoid misregister it is important that the cartonboard sheet is dimensionally stable (see "DIMENSIONAL STABILITY").

Dampening Solution

Used in wet offset printing. The dampening solution has three functions in offset printing:* to ensure that the ink does not adhere to the nonimage areas * to clean away cartonboard fragments * to cool down the process.Since dampening solution is required in offset printing, the dimensional stability and flatness of the cartonboard are important (See "DIMENSIONAL STABILITY" and "FLATNESS").

Varnish

There are different kinds of varnish, all of which have their own advantages and properties. A cartonboard surface is varnished to protect it against scratches or to stop it getting dirty. Varnish can also be used to emphasise the gloss of a design in whole or in part. The varnish is either applied to the cartonboard directly in the printing press or afterwards in a separate operation. Printing varnish - an oil-based varnish which is spread on in a printing press. Protects against scratches. Emulsion varnish - is spread on in the printing press at a varnishing station. Protects against scratches. UV varnish - is spread on either directly in the printing press or in a separate varnishing machine. Gives a glossy surface.

Printing Ink

Coloured pigment which is transferred from the printing plate with the aid of a vehicle (a carrier) and is then bound to the cartonboard surface with a binding agent such as resin.

Rubber Blanket

Coloured pigment which is transferred from the printing plate with the aid of a vehicle (a carrier) and is then bound to the cartonboard surface with a binding agent such as resin.

Printing Plate

The printing image used in offset printing

Abbreviations

WWF

World Wildlife Fund for nature

SETAC

Society of Environmental Toxicology and Chemistry.

RFID

Radio frequency identification device

LCA

Life cycle analysis.

ISO

International Standardisation Organisation.

INCPEN

Industry Council for Packaging and the Environment.

FSC

Forest Stewardship Council

FMCG

Fast Moving Consumer Goods

FAO

United Nations Food and Agricultural Organisation.

EUROPEN

A specialist agency dealing with packaging and environmental issues.

EMAS

The Eco-Management Scheme set up under the European Union. When this is awarded, it indicates that the organisation concerned is operating eco-management to the satisfaction of the awarding body. It is site specific, requires external certification and for the results to be published.

ECMA

European Carton Makers Association.

CEPI

The Confederation of European Paper Industries.

CEN

European Committee for Standardisation. Standards published by CEN are referenced with "EN" and the appropriate number.

BIR

Bureau of International Recycling

Pro Carton

Pro Carton is the European Association of Carton and Cartonboard manufacturers. Its main purpose is to promote the use of cartons and cartonboard to brand owners, the trade as well as designers, the media and politicians as an economically and ecologically balanced packaging medium.

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